Question: Find $h(x)$, with terms in order of decreasing degree, if  \[3x^4+2x-1+h(x)=5x^2-6x-1.\]
This equation is solved by \[h(x)=(5x^2-6x-1)-(3x^4+2x-1)=\boxed{-3x^4+5x^2-8x}\]